This invention relates to a direction and distance plotting device for use in air navigation. More particularly, the invention relates to a navigational plotter which is universally applicable for use with a variety of air navigation charts, whether they are sectional (SEC) or world air charts (WAC), or ONC charts. More particularly still, the navigational plotter is universally applicable for use with both sectional and WAC air charts, whether the scales on the charts are designated in units under the U.S. system or the metric system.
Air charts are generally sectional charts which are scaled 1 to 500,000, or WAC charts which are scaled 1 to 1,000,000. While there are navigational plotters presently commercially available that have both sectional and WAC scales on them, most of them are generally undesirable since the many scales printed thereon make it difficult to determine quickly which one of the many scales is to be used. Further still, most of these available navigational plotters have the scales printed or otherwise provided on them such that the scales are directly adjacent to each other and many times obscure the correct reading.
In view of the recent legal requirements for adopting the metric system in the United States, many air charts are or soon will be converted partially or totally to the metric system. As is normally the case, during the interim period, many aircraft pilots, as well as others, will find themselves having old charts which are scaled in the U.S. system and new charts which will be scaled in the metric system. They, therefore, will be confronted with the necessity of having at least two navigational plotters, one adapted for each of the respective system.
With reference to the navigational plotters that are presently commercially available, these plotters generally may be classified as conversion systems using adjacent scales for determining equivalent values. The process in using these plotters involves spotting the equivalent value and then counting graduations visually to determine the desired equivalents. This, in some cases, is more easily said then done. Holding a point by eye, and at the same time, counting from a calibrated graduation left or right can become quite difficult. This problem is solved on slide rules, for example, by the use of a movable hairline which holds the point of equivalence, while the graduations are counted to establish the conversion value. With a hairline, several scales can be crossed with ease. Obviously, it is not feasible to use such a movable hairline with multi-scale plotters of the type with which the invention is concerned. Therefore, in accordance with the present invention, a practical solution is provided in this invention by separating the scales laterally and providing a transparent gap between the individual scales, so that each scale may be positioned directly adjacent, for example, to a course line on a chart. This obviates the necessity for " eye-balling" across a plurality of scales, and reduces the possiblity of potentially dangerous errors. The invention further simplifies the construction of such plotters by printing all the necessary scales on one side thereof, thereby eliminating the two-sided or double-faced construction currently used, with the necessary concommitant increased cost.
In general, a plotter is a navigational tool which combines a straight-edge, for drawing course lines; scales for measuring distances; and a protractor for measuring directions. The construction of the plotter of the present invention provides two unobstructed straight edges, for drawing course lines and for laying off course lines in specific directions; a plurality of distance scales to correspond to the specific chart scales in use; and a 360.degree. protractor for measuring directions in conjunction with a North-South or meridian of longitude on a chart. It also provides a zero center correction scale for mechanically correcting for wind drift, compass variation and deviation. Also, as in all previous plotter patents issued to the present applicant, the distance scales are positioned below the straight edge. This construction conforms to the accustomed procedure in using a ruler, where the scales are customarily positioned below the straight edge of the ruler. Further still, the distance scales are appropriate to charts now in use by the air navigator and, additionally, include the kilometer scales which will become mandatory in the foreseeable future.
For the relatively slow aircraft, and in the circumstances where radio aid cannot be used and dead reckoning or pilotage navigation must be restored to, the sectional charts (scale 1 to 500,000) with their greater display of surface detail are, by far, the most suitable. The statute mile scale is appropriate for aircraft with airspeed indicators calibrated in miles per hours (mph); the nautical mile scale, likewise is appropriate for airspeed indicators calibrated in knots (nautical miles per hour). The kilometer scale is provided for aircraft operating in countries where the metric system is standard, and in countries like the United States where the metric system is gradually becoming mandatory. The world air chart (WAC) or ONC charts at a scale of 1 to 1,000,000 with a lesser display of service detail are, in essence, more suitable for relatively faster moving aircraft. The selection of the statute, nautical or kilometer scale, again, depends on the calibration of the airspeed indicator in the aircraft being flown, and in the country over which the aircraft is being flown. A unique feature of the plotter of the invention is the lateral separation of the various distance scales with transparent longitudinal gaps between them. This construction serves a two-fold purpose. First, it precludes the necessity for eye-balling across intermediate scales to obtain a desired reading. Any scale may be individually and separately placed directly under the course line and thus reduce or eliminate the possiblity of error.
The protractor component of the plotter consists of a zero to 360.degree. unit calibrated by a single scale clockwise, as is the method used in all navigational instruments such as magnetic compasses, peloruses, radio direction finders, small area plotting sheets, the compass roses printed on navigational charts, etc. With this type of plotter construction, only one mode of operation is required anywhere on the chart. By way of contrast, the half-circle plotter (180.degree.) protractor is calibrated in the wrong counter-clockwise direction and provides three modes of operation dependent upon the position of the plotter on the chart. Thus, the wrong direction of calibration, the ambiguity of two scales, and the three different modes of operation can and quite often do cause serious errors which by all means should be avoided!
In addition, the protractor of this invention incorporates a rectangular grid whose vertical lines are parallel to the North-South or zero to 180.degree. line direction of a protractor, and horizontal lines which are parallel to the East-West, that is, 90.degree. to 270.degree. line, on the p rotractor. Furthermore, each vertical line includes an arrowhead at the North end to facilitate orienting the protractor toward the top of the chart and to True North. To orient the protractor to True North on the chart the protractor is turned so that the grid lines are directly over or parallel to a meridian of longitude or a parallel of latitude. To add to the usefulness of the plotter of this invention, a zero center correction scale is provided to mechanically correct for and act as a check on wind-drift correction, and magnetic variation and deviation correction.
The plotter of the present invention represents the first major design improvement in such plotters in over 40 years. These improvements include for the first time two separate straight edges, six individual and isolated distance scales, that can be read one at a time, and a zero center scale for mechanically, rather than mentally, correcting for drift variation and deviation. Practical air navigation frequently requires simple interconversions of statutes, nautical and kilometer units of measurement for distances and speed. In fact, historically from the very beginning of early navigational computers, they included special indices for making such conversions.
Now, for the first time, the plotter of the invention can provide this basic and necessary requirement as an ancillary operation. The distance scales, inherently a part of the construction, provide easy conversions. For coarse readings, the WAC scales are appropriate, and for finer readings, the sectional scales are better suited. When scanning across the adjacent scales, a vertical line on the chart, such as a meridian of longitude or a North-South section line, very conveniently acts as a hairline, just like that on a straight slide rule.
Accordingly, it is an object of the present invention to provide an improved navigational plotter which not only is applicable for use with both sectional and WAC air charts but is applicable for use with both types of charts whether scaled in accordance with the present U.S. system or the metric system.
Further still, it is an object of this invention to provide a navigational plotter having the scales provided thereon in a fashion such that any one of the scales can be used without obscuring any desired distance scale or to require reading across various scales to obtain the proper measurement.
Still another object of this invention is to provide two zero-center correction scales to mechanically offset the normally encountered navigational errors of wind drift, magnetic variation and deviation. Also provided in this invention is a longitudinal line equidistant from the two longitudinal edges of the plotter, marked with two course index arrows to point out the course directions. Since all parallel lines have the same direction, the geometric directions of the parallel distance scales are all simultaneously indicated by the course index arrows.
Other objects of the invention will in part be obvious and will in part appear hereinafter.